Obstructive sleep apnea (OSA) is a common sleep disorder characterized by repetitive pharyngeal collapses resulting in extended pauses in breathing (apnea) or instances of abnormally low breathing flow (hypopnea) during sleep. Untreated OSA may result in neurocognitive impairments and cardiovascular complications including hypertension, heart failure, stroke, excessive daytime sleepiness, as well as increased risk of occupational and traffic accidents.
Severity of OSA is quantified by apnea hypopnea index (AHI), which is the number of apnea and hypopnea events per hour of sleep. An apnea event is defined as complete cessation of respiratory airflow for at least 10 s, whereas a hypopnea event is characterized by a decrease in airflow by 50% for 10 s. Apnea/hypopnea events usually result in a significant drop (>4%) in blood oxygen saturation level (SaO2). In OSA, by far the most common type of sleep apnea, breathing is interrupted despite respiratory effort, because the airway is physically blocked. In central sleep apnea (CSA), the effort to breathe is weak or absent. Mixed sleep apnea is a combination of OSA and CSA.
An estimated 2-7% of women and 4-14% of men over 30 years of age have moderate to severe OSA. However, most OSA patients are not clinically diagnosed. A major study in the United States found that in a population with access to a sleep disorders clinic, more than 80% of middle-aged men and women who suffered from moderate or severe OSA had not been diagnosed. Undiagnosed OSA negatively impacts overall health and quality of life, is associated with increased risk of accidents, and is very costly to the medical system. The mean annual medical cost of an undiagnosed OSA patient is estimated to be approximately twice that of a non-OSA individual, accounting for several billion dollars in additional annual medical costs in the U.S. alone.
Currently, standard testing for OSA involves overnight polysomnography (PSG) in a sleep laboratory. PSG includes simultaneous recording of electroencephalogram, electrooculogram, electromyogram of chin and anterior tibialis, respiratory airflow, electrocardiogram, pulse oximetry, and snoring sounds. Because PSG is expensive, time-consuming, and inconvenient, many patients with OSA are not diagnosed or treated.
Thus, there is a need in the art for improved methods of diagnosing OSA. The present invention satisfies this demand.